Precision grinding machine



Dec. 2, 1941. A. J. DEVLIN PRECISION GRINDING MACHINE Filed May 8, 1940 8 Sheets-Sheet 1;

INVENTOR A.J Devhn/ ATTORNEY Dec. 2, 1941. 7i. J. DEVLIN PRECISION GRINDING "MACHINE Filed May 8, 1940 8 Sheets-Sheet 2 INVENTOR A.Jfie0li70 ATTORNE Dec. 2, 1941.

A. J'. DEVLIN PRECISION GRINDING NAcHINE Filed May 8, 1940 8 Sheets-Sheet 3 ATTORNEY Dec. 2, 1941. A. J. DEVLIN 2,264,302

PRECISION GRINDING MACHINE Filed May 8, 1940 -8 Sheets-Sheei 4 INVENTOR A. Devlin ATTORNW 8 Sheets-Sheet 5 I INVIENTOR BY Bsviiw WQMW ATTORNEY Dec. 2, 1941. A. J. DEVLIN PRECISION GRINDING MACHINE Filed May' 8, 19.40

8 Sheets-Sheet 6 Filed May 8, 1940 INVENTOR J1 evlm/ ATTORNEY Dec. 2, 1941. A, DEVLIN 2,264,302

PRECISION GRINDING MACHINE Filed May 8, 1940 8 sheet s-shee'l, '7

ATTORNEY Dec. 2, 1941 A. J. DEVLIN v PRECISION GRINDING MACHINE Filed'ma s, 1940 a Sheets-Sheet 8 INVENTOR A.J.De0lv7v ATTORNEY WWW . grinding wheel carriage to throw out Patented Dec. 2, 1941 UNITED STATES PATENT OFFICE 2,264,302 PRECISION GRINDING MACHINE Arthur J. Devlin, Washington, D. 0.

Application May 8, 1940, Serial No. 333,994

(Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 15 Claims.

This invention relates to a grinding machine and more particularly to a machine for grinding the edges of optical lenses to reduce such lenses accurately to a predetermined size, that Fig. 9 is a bottom plan view of a portion of the grinding wheel carriage.

To provide automatic means to stop the grind- 2 ing at a predetermined diameter of the piece being worked upon, which means is jointly controlled by the linear travel of the carriage and by the rotation of the feed screw that moves the carriage;

To provide a machine as described that requires no attention of the operator between the initiation of the grinding and the completion of the grinding to the size for which the machine is set; and

To provide a machine for grinding simultaneously a plurality of lenses of the same size.

In the drawings:

Fig. l is a top plan view of my novel grinding machine;

Fig. 2 is a transverse sectional elevation on the line 33, Fig. 5, looking in the direction of the arrow and showing the travelling nut for driving the grinding wheel carriage and my novel precision anti-friction guideways;

Fig. 3 is a sectional view taken transversely of the feed screw, substantially on the line 3-3, Fig. 6;

Fig. 4 is an enlarged detailed elevation of the means for driving the feed screw;

Fig. 5 is a top plan view of the bed for the grinding wheel carriage;

Fig. 6 is an elevational section taken substantially along the axis of the feed screw for the grinding wheel carriage;

Fig. 7 is an end elevation view of the carriage for the work-piece holding spindle;

Fig. 8 is a, detailed elevational view of the mechanism controlled by the position of the one of the feed pawls; and

Referring now to the drawings, it will be seen in Fig. 2 that my machine comprises a base in supporting a bed II for the work-holding spin dle carriage l2 and a bed l3 at right angles thereto for the grinding wheel carriage M. A motor 15 drives the worm is meshed with the worm gear wheel ll mounted on a shaft I8 whereby the work-piece holding spindle I9 is driven. The spindle I9 is connected to the shaft' ill by means of a crosshead 20 fixed on spindle 19 that is slidable in the longitudinal slot 2| formed in a sleeve 22 fixed to shaft i8, whereby the spindle I9 is positively driven and simultaneous reciprocation of the carriage I2 is permitted.

A boot 23 is fitted around sleeve 22 to exclude dirt and grit from the slot 2 I.

The train 24 of reducing gears drives a shaft 25 whereon is keyed a beveled pinion 26 meshed with another beveled pinion -21 fixed on a shaft 28 that has the pinion 29 fixed thereon. A gear 30 is meshed with pinion 29 and has in its upper face a diametral slot 3| in which a crank pin 32 is adjustable. The link 33 is pivoted at one end on the crank pin 32 and at its other end is pivotally connected to a pin 34 fixed to carriage l2 jwhereby rotation of the gear 30 reciprocates the It is essential that the carriage I2 have a true rectilinear travel along the same line over long periods of use. To insure this, I have devised the novel anti-friction precision guideways that will now be described in connection with Fig. 3. While Fig. 3 shows the structure connected with the grinding wheel carriage It, it is to be understood that the anti-friction guideways are identical in both carriages l2 and It, the former being shown in Fig. 7 where corresponding parts have the same reference characters as in Fig. 3.

The bed l3 has formed in it two upwardly facing channels 35 and 36 in each of which channels is disposed a pair of accurately cylindrical hardened rods 31 slightly spaced from and accurately parallel to each other. rality of hardened balls 38 is disposed between the rods 31, the several balls being kept spaced from each other by a member 39, there being a group of spaced balls at each end of member 39. The purpose of spacing the balls 38 is to prevent the balls from rolling into contact with A pluone another and thus setting up unnecessary friction. One side of the carriage M has formed in it a channel 40 wherein are disposed a pair of accurately cylindrical hardened rods 3'! so disposed that when th carriage I4 is assembled on bed i3 the balls 38 will ride between the rods 31'. As is shown in Fig. 9, the rods 3'! have circumferential grooves 4| formed therein to receive a screw 42 whereby the rods 31' are secured in carriage 14, the grooves permitting the head of screw 42 to be kept out of contact with the balls 38. At the other side of carriage 84 a removable hardened track -member 43 is inserted in carriage 14 to ride upon the balls 38. A skirt I4 at each side prevents access of dirt to the guideways.

Rising of carriage i4 is prevented by the holding-down members 44 secured to carriage 14 by threaded studs 45. Hold-down piece 44 has hardened track portions upon which the balls 38' roll, the upper sides of the balls bearing against hardened track portions 46 set in bed l3. It is thus apparent that my novel guideways provide substantially frictionless support for the reciprocating carriage and cause the carriage to move along a true rectilinear path. The rods 31 and 31' may be rotated a few degrees about their longitudinal axes to compensate for any wear which may occur and thus provide a large number of fresh supporting surfaces. The balls 38 are carefullychosen in sets of accurately identical size.

The work-piece is attached to spindle I9 by any form of chuck 41 well known in the art.

However,-I have provided the means for grinding simultaneously several lenses of the same size. Bracket 48 is fixed at one end to carriage l2 and has at its other end a down-turned portion 49 wherein a second chuck 4'! is suitably mounted against anti-friction thrust bearings (not shown). A screw 58 is threaded in the portion 49 and bears against a member that carries the thrust bearings. A plurality of lenses -52 are held between the chuck 41 and 41' to be operated upon by the abrasive wheel 53.

The abrasive wheel 53 is rotatably mounted on carriage l4 and is driven by a motor 54, likewise mounted on carriage l4, through the pulleys 55 and 56 connected by belt 51. Carriage I4 is traversed on bed l3 by means of a feed screw 58 mounted in bed I3 to be freely rotatable but to prevent longitudinal movement of the screw. The shaft 25 carries a beveled pinion 59 meshed with a beveled pinion 60 secured on the same shaft as a disk (H which has in its face a slot 62 wherein a rank pin 53 is slidably mounted and is adjustable by means of a screw 64. A link 85 is connected at one end to crank pin 63 and at its other end to a feed lever 68 that is mounted to oscillate about the axis of feed screw 58 and carries at its upper end two feed pawls 87 and 88.

Secured on feed screws 58 is a driving disk 69 having on its periphery a plurality of accurately spaced ratchet teeth 10. In one embodi- 58 to provide for manual operation of the feed screw for setting the same.

A dial 13, graduated in 200 parts corresponding to the ratchet teeth 10 is fixed to the ratchet wheel 69. The feed stop arm 14 is, by means of a 'screw 15, adjustably fixed on the axially elongated hub of disk 69 and has a portion I6 extending over the edge of the perlphery of disk 69 to lift feed pawl 57 out of engagement with teeth 18 at a predetermined angular position of the disk 69, the disengaging of the pawl 61 being determined by the graduation on dial 13 corresponding to the setting of portion 15. It is apparent that the disengagement of pawl 51 will not by itself arrest the actuation of feed screw 58 because the pawl 68 will continue to actuate the ratchet wheel 59! The purpose of this construction is to permit the machine to operate through more than one complete rotation of the feed screw 58.

The kick-out arm 11 is mounted to oscillate about the axis of feed screw 58 and carries a pin 18 that extends over the edge of the periphery of ratchet wheel 69 to disengage pawl 68 under conditions that will be hereinafter described. A contractile spring I9 has one end fixed and the other end attached to a pin 80 carried by kickout arm 11 and tends to move the arm 11 back toward the pawl 68. During operation the kickout arm 11 is held away from pawl 68 through engagement of the pin 80 in a notch 8| in latch 8| which is secured on a shaft 82 that is rockably mounted on bed l3. In shaft 82 there is formed a recess 83 that is laterallyoffset from the axis of shaft 82 and in which one end of pin 84 is seated An adjustable dog 85 is fixed to carriage l4 and at the desired point in the traverse of carriage l4 it contacts pin 84 and rocks shaft 82 to disengage latch 8| from pin 80, against the effort of spring pressed plunger 86 that tends to hold latch 8| engaged with pin 88. When latch BI is so disengaged kick-out arm TI is rocked back by spring 19 and pin 18 lifts pawl 68 out of engagement with teeth 10 and retains pawl 68 disengaged until the arm 11 is manually reset. It is apparent that after pawl 68 has been thus disengaged at the predetermined point in the travel of carriage 14, when feed stop arm 14 next disengages pawl 61 from teeth 10, the actuation of feed screw 58 will be arrested. A fixed index 18! provides a reference point for setting the feed stop arm 14.

It frequently occurs that a feed screw, such as screw 58, becomes deformed so that the axis thereof is not a true straight line and in such cases the travelling nut driven by the screw is given a movement transversely of the axis of the screw. If the travelling nut is rigidly connected to the carriage propelled thereby, stresses are applied to the carriage that result in strains in or breakage of parts thereof, the guideways are worn excessively and both the screw and the travelling nut may be damaged. The form of travelling nut next to be described eliminates the above-mentioned bad effects.

As is clearly shown in Figs. 3, 5 and 6, the traveling nut 81 is provided with two pairs of spaced apart ears 88 and 89 on opposite sides of the axis of screw 58 and the downwardly extending projections 90 from carriage l4 lie between the ears of the respective pairs. Each ear 88 carries a fixed pin 92 having a flat face that bears against the respectively adjacent projection 90'and each car 89 has threadedly engaged with it a screw 93 likewise having a flat end that is sent up against the projection 90 with a firm, but not frictionally binding, contact. This results in a positive drive of the carriage without any lost motion longitudinally of the screw 58 but permits the projections 90 to move between the pins 92 and screws 93, transversely of screw 58, to compensate for any warping of screw 58. Nut ill is prevented from rotating with screw 56 by a pin 94 and a screw 95 that bear upon a member 96 fixed in a projection 97 on the carriage l5. Owing to differences in the hardness an structure of abrasive wheels, the grindlng'faces of such wheels require dressing and trueing at intervals. I show in Fig. 1 a means for trueing the face of the wheel 53 to insure that the said face will be transversely fiat and a line on such face parallel to the axis of the wheel will be accurately parallel to the axis of work spindle l9. The dressing tool 98, preferably a diamond of a type well known in the art, is mounted on a tool holder 99 adjustably fixed to carriage l2 by means of a clamping screw I00. When wheel 53 is to be dressed, the tool holder 99 is adjusted to the right, as seen in Fig. 1, so that reciprocation of carriage l2 will cause the tool 98 to move back and forth across the wheel 53 and the wheel 53 is revolved in contact with tool 98 for a suihcient time to dress the face of wheel 53.

When a lens is to be ground it is attached to a chuck in any manner known in the art and the chuck is engaged with the driving spindle l9. Inasmuch as the details of these parts are old and ,well known no further description is deemed necessary. Hand wheel H is operated to traverse carriage I6 and bring grinding wheel 53 into contact with the edge of the lens blank. The operator, having measured the blank and knowing how much material has to be removed to reduce the blank to the desired size, adjusts the dog 85 to permit the carriage Hi to move toward the work approximately the required distance and the feed stop arm 78 is set to throw out the pawl 67 shortly after pawl 68 has been rendered inoperative by the action of dog 85 and the mechanism operated thereby.

' When the feed screw has been stopped after the completion of the preliminary grinding, the

operator measuresthe blank with a micrometer and sets the feed stop arm M a sufiicient number of graduation devices on dial 13 to permit the carriage Hi to be traversed the necessary distance to reduce the lens blank accurately to size. In this final grinding operation, the pawl 68 is held disengaged by connection with arm T! and consequently when portion 16 of arm 741 rides under pawl 61 the feed screw is stopped. A shield, comprising the telescoping members 9! and SI, protects screw 58 from material abraded by wheel 53 and from other dirt.

The distance travelled by carriage l2 in its reciprocating movement is varied by changing the position of crank pin 32. If a single lens is to be may be used and/or manufactured by or for the I Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

I claim: 1. A precision grinding machine, comprising a first bed, a first reciprocable carriage; anti-fric- I} tion guideways for mounting said carriage on said bed including a pair of accurately cylindrical hard members parallel to and somewhat spaced from each other carried by one side of said bed, a plurality of hard balls of uniform size contacting I both said members and retained spaced from each other, a like pair of hard cylindrical memmembers, and a hardened track member carried by the other side of said carriage contacting the hard balls at the other side of said bed; a workpiece holding spindle rotatably mounted in said carriage and driving means connected to rotate said spindle and reciprocate said carriage; a second bed at right angles to said first bed, a second reciprocable carriage, and anti-friction guideways as above described whereby said second carriage is mounted on said second bed, an abrasive wheel rotatably mounted on said second carriage to operate upon a work piece carried by said spindle, means to drive said abrasive wheel, a feed screw mounted in said second bed connected to said second carriage to traverse said second carriage on said second bed, means actuated by said spindle driving means to rotate said feed screw, and automatic means to arrest the rotation of said feed screw including an instrumentality operated by said second carriage at a predetermined point in the traversing movement of said second carriage and a second instrumentality operated by said feed screw ata predetermined angular position of said feed screw, the simultaneous functioning of both said instrumentalities being required to arrest the rotation of said feed screw.

2. A precision grinding machine, comprising a thereon, a work-piece holding spindle rotatably ground at one operation the pin 32 is set relamounted in said carriage, a device connected to drive said spindle and reciprocate said carriage;' a second bed, a second carriage reciprocably mounted thereon, a feed screw-rotatably mounted in said second bed, means connecting said screw to said second carriage, an abrasive wheel rotatably mounted on said second carriage'to operate upon a work-piece carried by said spindle; a disk fixedly connected to said screw and having accurately spaced peripheral ratchet teeth, an oscillatable feed lever mounted adjacent said disk, two pawls pivoted to said lever to be engageable with said teeth, means connecting said lever to said driving device to oscillate said lever, a feed stop arm fixable to rotate with said disk and having a portion to render one said pawl inoperative at a selected point in the rotation of said disk, at rockable kick-out arm having a portion to render the other said pawl inoperative when said kickout arm is in one position, a spring connected to move said kick-out arm to said one position, a shaft rockably mounted in said second bed; a latch fixed to said shaft engageable, with said kick-out arm to hold said kick-out arm in another position, said shaft having in it a recess laterally ofiset from the axis of said shaft, 9. pin bearing on the bottom of said recess, a dog on versely of the axlsoisaid screw while preventing i 1 lost motion therebetween parallel to saidaxis, i Pi 1 a wheel having ratchet teeth :drivingly connected to said screw,anoscillatablefeed lever mounted 1 1 1 1 1 1 1 said second carriage to engage said pin and rock ===1 1 11 11 1 1 1 1 said shaft to disengage saidlatch from said kick- 1. 1

1 out arm at a predetermined pointinthe traverse 1 1 of said 'secondcarriage, and means mounted on 1 11 11 11 1 1 1 said second carriage todrive said abrasive wheel, 6 adjacent said wheel, two pawlspivotedtosaid I 3 A precision grinding machine, comprising a 1 lever to engage said teeth, driving means to oscll- 1 1 1 1 1 1 1 first bed,1a first carriage reciprocably mounted 1 late said lever, a feed stop arm fixable to rotate 1 1 1 1 1 1 thereon, a work-piece holding spindle rotatably 1 withsaid wheel and having a portion torender mounted in said carriage, adevice connectedto one said pawl inoperative at a selected point in 1 1 1 1 1 1 1 1 1 1 1 drive said spindle and reciprocate saidcarriage; 10 the rotationof said wheel; a rockable kick-out 1 11 11 11 1 1 1 1 a second bed, a second carriage reciprocably arm having a portion to render the other said 1 1 mounted thereon, a feedscrewrotatably mount- 1 pawl inoperative in one position of said kick-out 1 1 1 1 1 1 1 1 1 1 1 :ed in said second bed, means connecting said arm, aispringconnectedto movesaid kick-out 11 11 11 1 1 1 1 1 1 1 1 1 screw to said second 1carriage,: an abrasive wheel arm to said one position, a shaftrockablymount rotatably: mounted on said second carriage to 15 :ed in said bed, a latch fixed to said shaft err-' 1 1 1 1 1 1 1 1 1 1 -gageablei withsaidkickout arm to hold said dle; a disk fixedly connected to said screw and hick-out arm in another position, said shafthav 1 1 1 1 1 1 having: accurately spaced 1 peripheral ratchet 1 i ing in it a recess laterally offset from the axis 1 1 1 1 1 1 1 1 1 teeth, an oscillatable feed lever mounted adjacent of said shaft, a pin hearing on the bottom of said disk, two pawls pivoted to said lever to be said recess, a dog on said carriage to engage said engageable with said teeth, means: connecting 1 pin and rock said shaft to disengage said latch said lever to saiddriving device to oscillate said 1 1 from said kick-out arm at a predetermined point 1 lever, afeed stop armfixableto rotate with said. in the traverse of said carriage, and means to disk andhaving 1a portion to render one said v drive said abrasive wheel; 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 1 pawl inoperativeat a selected'point in the rota- 1 16.i In a precision 1grinding1 machine, a bed, a

1 tionof said dislga rockable kick-out arm having 1 carriage, anti-friction guideways whereby said 1 1 aportionito render theothersaid pawl inoper- :carriageis reciprocably mounted on said bed, a 11 feed iscrew rotatably mounted said bed, a i i operate upon a work-piece carried by said spin-1 1 i 1 gage said latch from said kick-out arm atapre- I determinedpoint inthje traverse of said second 1 1 1 1 1 1 ativewhensaidkick-out arm is in one positiom 1 a spring connected to move-said kick-out arm 1 to said :one position, a shaft rockably mounted in said second bed, a swingable latch engageable 1 i with said kick-out arm to hold said: kick out arm 1 in another position; and means 1 including an ele- 1 ment mounted on said secondcarriage to disen-i I carriage.

, 1 4. A precision grinding machine, comprising a 1 firsti bed, a first carriage reciprocably 1 mounted thereon, a work-piece holding spindle rotatably mounted in said carriage,- a device connected to a second bed, a second carriage reciprocably mounted thereon, a feed screw rotatably mounted in said second bed, means connecting said screw to said second carriage, an abrasive wheel rotatably mounted on said second carriage to operate upon a work-piece carried by said spindle; a disk fixedly connected to said screw and having accurately spaced peripheral ratchet teeth, an oscillatable feed lever mounted adjacent said disk, two pawls pivoted to said lever to be engageable with said teeth, means connecting said lever to said driving device to oscillate said lever, a feed stop arm fixable to rotate with said disk and having a portion to render one said pawl inoperative at a selected point in the rotation of said disk, a rockable kick-out arm having a portion to render the other said powl inoperative when said kick-out arm is in one position, a spring connected to move said kick-out arm to said one position, a shaft rockably mounted in said second bed, means engageable with said kickout arm to hold said kick-out arm away from said one position, and means including an element mounted on said second carriage to disengage said holding means at a predetermined point in the traverse of said second carriage.

5. In a precision grinding machine, a bed, a carriage, anti-friction guideways whereby said carriageis reciprocably mounted on said bed, a feed screw rotatably mounted in said bed, a travelling nut on said screw, means connecting said nutto said carriage to permit relative movement between said nut and said carriage transment between said nut and said carriagetrans i i versely of the axis of said screw while preventing 1 travelling nut on said screw, means connecting saidnut to said carriage to-p'ermit relative movelost motion therebetween parallelto said axis, a

wheel having ratchet teeth :drivingly connected i i i to said screw, an oscillatable feed lever mounted 11 11 11 adjacent said wheel, two pawls pivoted to said le- 1 ver to engage: said teeth, driving means to oscillate said lever,afeed stop arm fixable' to rotate 11 11 11 T i with said wheel and having .a. portion to render 1 one said pawl, inoperative Eat a selected point in i the rotation of said wheel, a rockable "kick-out 11 drivesaid spindle andreciprocate said carriage;

arm having a portion to render the other said pawl inoperative in one position of said kick-out arm, a spring connected to move said kick-out arm to said one position, means engageable with said kick-out arm to hold said kick-out arm away from said one position, and means including an element mounted on said carriage to disengage said holding means at a predetermined point in the traverse of said carriage.

7. In a precision grinding machine, a bed, a carriage, anti-friction guideways whereby said carriage is reciprocably mounted on said bed; a feed screw rotatably mounted in said bed, a travelling nut on said screw, means connecting said nut to said carriage to permit relative movement between said not and said carriage transversely of the axis of said screw while preventing lost motion therebetween parallel to said axis, a wheel having ratchet teeth drivingly connected to said screw, an oscillatable feed lever mounted adjacent said wheel, two pawls pivoted to said lever to engage said teeth, driving means to oscillate said lever, means carried by said ratchet wheel to render one said pawl temporarily inoperative at a predetermined point in the rotation of said wheel, and means including an element mounted on said carriage to render the other said pawl inoperative, until manually reset, at a predetermined point in the traverse of said carriage.

8. A machine as described, comprising a rotatably and reciprocably mounted work-piece holding spindle, mechanism to rotate and reciprocate said spindle, a carriage'mounted for traversing movement toward a piece of work held by said spindle, an abrasive wheel rotatably mounted on said carriage and positioned to operate on a work-piece held by said spindle, means to drive said wheel, feed means to move said wheel toward said work at a predetermined rate, means drivingly connecting said feed means to said mechanism; and means to arrest operation of said feeding means while said mechanism continues to operate, said arresting means, including a mechanica1 train actuated at a predetermined point in the travel of said carriage and a device functioning at a predetermined position of said feeding means, the simultaneous action of both said train and said device being required to arrest operation of said feeding means.

9. In a precision machine having a bed and a carriage, anti-friction guideways whereby said carriage is reciprocably mounted on said bed comprising a pair of accurately cylindrical hard members parallel to and slightly spaced from each other carried by one side of said bed, a like pair of members carried by the same side of said carriage, a plurality of hard balls disposed between the members of each pair and between said two pairs, a second pair of like cylindrical members carried by the other side of said bed parallel to said first-mentioned pair, a plurality of hard balls disposed between the members of said second pair, a removable hardened track member carried by the other side of said carriage to ride upon the balls between said second pair of cylindrical members, and means to prevent upward displacement of said carriage during operation of said machine.

10. In a precision machine having a bed and a carriage of considerable weight, an anti-friction guideway for reciprocably mounting said carriage upon saidbed comprising a pair of accurately cylindrical hard members parallel to and slightly spaced from each other carried by said bed, a like pair of cylindrical members carried by said carriage, and a plurality of hard balls disposed between the members of each pair and between said pairs, said cylindrical members being adjustable about their longitudinal axes to present new contact areas to said balls.

11. In a precision machine having a bed and a carriage of considerable weight, anti-friction guideway for reciprocably mounting said carriage upon said bed comprising a pair of accurately cylindrical hard members parallel 'to and slightly spaced from each other carried by said bed, a plurality of hard balls disposed between said members, and a hardened track member carried by said carriage to ride upon said balls, said cylindrical members being adjustable about their longitudinal axes to present new contact areas to said balls. 7

12. In a machine having a bed and a carriage traversable thereon, a feed screw rotatably mounted in said bed, said carriage having a projection extending down on each side of said screw and said projections being transversely alined, a travelling nut threadedly engaging said screw, two pairs of ears on said nut so positioned that a respective one of said projections.

lies between the ears of each said pair, a fixed pin carried by one ear of each pair extending toward the respectively adjacent projection and an adjustable screw carried by the other ear of each pair, whereby each said projection is held between a fixed pin and an adjustable screw with positive but not frictionally binding contact to permit relative movement between said carriage and said nut transversely of said screw while preventing lost motion between said projections and said nut, and positive but not frictionally binding means connecting said nut to said carriage to prevent rotation of said nut with said screw.

13; In a machine having a bed and a carriage traversable thereon, a feed screw rotatably mounted in said bed, said carriage having a projection extending down on each side of said screw and said projections being transversely alined, a travelling nut threadedly engaging said screw, means drivingly connecting said nut to said projections to permit relative movement between said nut and said carriage transversely of said screw while preventing lost motion between said nut and said projections longitudinally of said screw, and means connecting .said nut to said carriage to permit relative movement between said nut and said carriage transversely of said screw while preventing rotation of 'said nu; with said screw.

;14. A grinding machine, comprising a reciprocably and rotatably mounted work-piece holding spindle, a reciprocable carriage, a grinding device carried by said carriage to operate upon a work-piece carried by said spindle, a feed screw, means drivingly connecting said carriage to said screw, said connecting means permitting relative movement between said screw and said carriage transversely of said screw while preventing lost motion longitudinally of said screw, means to rotate said screw, and means to arrest operation of said screw rotating means controlled jointly by the position of said carriage in its travel and by the angular position of said feed screw.

15. In a precision machine having a bed and a carriage accurately slidable thereon, a rotatable screw mounted to prevent longitudiai movement of said screw, a travelling nut on said screw, and means drivingly connecting said nut and said carriage to permit relative movement between said nut and said carriage transversely of said screw while preventing lost motion between said nut and said carriage.

' ARTHUR J. DEVLIN. 

